1. Field of the Invention
This invention relates to a disc-shaped information recording medium for optically recording/reproducing the information, such as an optical disc.
2. Description of the Related Art
Among optical disc systems in which a recording/reproducing track on a recording surface is scanned by a laser beam for recording/reproducing various data, there are a CLV system in which the optical disc is rotated at a constant linear velocity for recording/reproducing data, a CAV system in which the optical disc is rotated at a constant angular velocity for recording/reproducing data, and a MCAV system (modified CAV system) in which the spatial recording density is set so as to be substantially equal in both the inner and outer rims of the disc for increasing the recording density.
Heretofore, in the optical disc, either a land or a groove, formed concentrically or spirally on the recording surface, is used as a recording/reproducing track. In general, a spirally formed land is used as the recording/reproducing track TR.
There is also known a continuous servo system in which a pre-groove continuously formed along the track is used for tracking control, or a sampled servo system in which servo areas discretely formed on the track are utilized for tracking control. With the continuous servo system, the land is tracked using an optical phase difference between the land and the groove for recording/reproducing the information on or from the land, that is the recording/reproducing track.
On the recording/reproducing track, an address section is formed for recording management information for data recording/reproduction.
FIG. 2 shows the structure of an address section of an optical disc of the continuous servo system prescribed by ISO (International Organization for Standardization).
In the structure of the address section, shown in FIG. 2, VFO denotes a clock seizing signal containing a large quantity of the phase information for locking the PLL (phase locked loop) of the clock reproducing system for extracting clocks for reproducing address information, AM denotes synchronization signals for taking the timing for reproducing the address information and ID denotes the actual address information containing the error correction codes. The address section may be comprised of a plurality of sets of the above signals. In the example of FIG. 2, the above sets of signals are recorded in triplicates. The address section may be preceded by a signal SM specifying the leading end of the section.
Among known optical discs, there are a so-called ROM disc, dedicated to reproduction, a recordable RAM disc, such as a write-once disc or a magneto-optical disc, and a so-called hybrid disc having both a ROM area and a RAM area.
If, for the purpose of increasing disc capacity, the track pitch is reduced for increasing the density in the radial direction, the problem of cross-talk between tracks arises. In particular, embossed pits formed by pre-formatting seriously affect neighboring tracks.